4 Advanced usage

Multiple compressed files can be concatenated. In this case,
gunzip will extract all members at once. If one member is
damaged, other members might still be recovered after removal of the
damaged member. Better compression can be usually obtained if all
members are decompressed and then recompressed in a single step.

This is an example of concatenating gzip files:

gzip -c file1 > foo.gz
gzip -c file2 >> foo.gz

Then

gunzip -c foo

is equivalent to

cat file1 file2

In case of damage to one member of a ‘.gz’ file, other members can
still be recovered (if the damaged member is removed). However,
you can get better compression by compressing all members at once:

cat file1 file2 | gzip > foo.gz

compresses better than

gzip -c file1 file2 > foo.gz

If you want to recompress concatenated files to get better compression, do:

zcat old.gz | gzip > new.gz

If a compressed file consists of several members, the uncompressed
size and CRC reported by the --list option applies to
the last member
only. If you need the uncompressed size for all members, you can use:

zcat file.gz | wc -c

If you wish to create a single archive file with multiple members so
that members can later be extracted independently, use an archiver such
as tar or zip. GNUtar
supports the -z
option to invoke gzip transparently. gzip is designed as a
complement to tar, not as a replacement.